Processing of data to determine compatability in an input/output processing system

ABSTRACT

A computer program product, an apparatus, and a method for processing communications between a control unit and a channel subsystem in an input/output processing system are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method including: sending a message from the channel subsystem to the control unit in a first mode; receiving a response from the control unit and determining from the response whether the control unit supports a message protocol; and responsive to the message protocol being supported by the control unit, sending another message using the message protocol from the channel subsystem to the control unit to determine whether the control unit supports a second mode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates generally to input/output processing, andin particular, to coordinating protocol compatibility and operationsassociated with input/output processing.

2. Description of Background

Input/output (I/O) operations are used to transfer data between memoryand I/O devices of an I/O processing system. Specifically, data iswritten from memory to one or more I/O devices, and data is read fromone or more I/O devices to memory by executing I/O operations.

To facilitate processing of I/O operations, an I/O subsystem of the I/Oprocessing system is employed. The I/O subsystem is coupled to mainmemory and the I/O devices of the I/O processing system and directs theflow of information between memory and the I/O devices. One example ofan I/O subsystem is a channel subsystem. The channel subsystem useschannel paths as communications media. Each channel path includes achannel coupled to a control unit, the control unit being furthercoupled to one or more I/O devices.

The channel subsystem may employ channel command words (CCWs) totransfer data between the I/O devices and memory. A CCW specifies thecommand to be executed. For commands initiating certain I/O operations,the CCW designates the memory area associated with the operation, theaction to be taken whenever a transfer to or from the area is completed,and other options.

During I/O processing, a list of CCWs is fetched from memory by achannel. The channel parses each command from the list of CCWs andforwards a number of the commands, each command in its own entity, to acontrol unit coupled to the channel. The control unit then processes thecommands. The channel tracks the state of each command and controls whenthe next set of commands are to be sent to the control unit forprocessing. The channel ensures that each command is sent to the controlunit in its own entity. Further, the channel infers certain informationassociated with processing the response from the control unit for eachcommand.

Currently, there is no link protocol that allows for the exchange ofoperating parameters between the channel and the control unit, andallows the control unit to request that new commands be ceased for aselected period of time. Typically, current link protocols require thateither the channel cease sending new commands, or that the control unitrespond to new commands with a busy message. However, such busy messagesmay result in errors and possible loss of the logical path establishedbetween the control unit and the channel.

Accordingly, there is a need in the art for protocols to allow for theexchange of selected operating parameters and to allow the control unitto request suspension of commands for a selected time period.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention include a computer program product forprocessing communications between a control unit and a channel subsystemin an input/output processing system. The computer program productincludes a tangible storage medium readable by a processing circuit andstoring instructions for execution by the processing circuit forperforming a method including: sending a message from the channelsubsystem to the control unit in a first mode; receiving a response fromthe control unit and determining from the response whether the controlunit supports a message protocol; and responsive to the message protocolbeing supported by the control unit, sending another message using themessage protocol from the channel subsystem to the control unit todetermine whether the control unit supports a second mode.

Additional embodiments include an apparatus for processingcommunications in an input/output processing system. The apparatusincludes a channel subsystem of a host computer system in communicationwith a control unit capable of commanding and determining status of anI/O device. The channel subsystem performs: sending a message to thecontrol unit in a first mode; receiving a response from the control unitand determining from the response whether the control unit supports amessage protocol; and responsive to the message protocol being supportedby the control unit, sending another message using the message protocolto the control unit to determine whether the control unit supports asecond mode.

Further embodiments include a method of processing communicationsbetween a control unit and a channel subsystem in an input/outputprocessing system. The method includes: sending a message from thechannel subsystem to the control unit in a first mode; receiving aresponse from the control unit and determining from the response whetherthe control unit supports a message protocol; and responsive to themessage protocol being supported by the control unit, sending anothermessage using the message protocol from the channel subsystem to thecontrol unit to determine whether the control unit supports a secondmode.

Still further embodiments include a computer program product forprocessing communications between a control unit and a channel subsystemin an input/output processing system. The computer program productincludes a tangible storage medium readable by a processing circuit andstoring instructions for execution by the processing circuit forperforming a method including: sending an identification request messagefrom the channel subsystem to the control unit in a first mode, thefirst mode using a first protocol supporting Channel Command Words(CCW); receiving an identification request response from the controlunit, the response comprising a bit in a field that indicates whether aProcess Log-in (PRLI) message protocol is supported; determining fromthe bit whether the control unit supports the PRLI message protocol;responsive to the PRLI message protocol being supported by the controlunit, sending another message using the PRLI message protocol from thechannel subsystem to the control unit to determine whether the controlunit supports a second mode, the second mode using a second protocolsupporting Transport Control Words (TCW); and initiating input/outputoperations to the control unit using the second mode.

Other apparatuses, methods, and/or computer program products accordingto embodiments will be or become apparent to one with skill in the artupon review of the following drawings and detailed description. It isintended that all such additional systems, methods, and/or computerprogram products be included within this description, be within thescope of the present invention, and be protected by the accompanyingclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of an I/O processing system incorporatingand using one or more aspects of the present invention;

FIG. 2 a depicts one example of a prior art channel command word;

FIG. 2 b depicts one example of a prior art channel command word channelprogram;

FIG. 3 depicts one embodiment of a prior art link protocol used incommunicating between a channel and control unit to execute the channelcommand word channel program of FIG. 2 b;

FIG. 4 depicts one embodiment of a transport control word channelprogram, in accordance with an aspect of the present invention;

FIG. 5 depicts one embodiment of a link protocol used to communicatebetween a channel and control unit to execute the transport control wordchannel program of FIG. 4, in accordance with an aspect of the presentinvention;

FIG. 6 depicts one embodiment of a prior art link protocol used tocommunicate between a channel and control unit in order to execute fourread commands of a channel command word channel program;

FIG. 7 depicts one embodiment of a link protocol used to communicatebetween a channel and control unit to process the four read commands ofa transport control word channel program, in accordance with an aspectof the present invention;

FIG. 8 depicts one embodiment of a control unit and a channel, inaccordance with an aspect of the present invention; and

FIG. 9 depicts one embodiment of a process for identifying a compatiblecontrol unit of an I/O processing system using data from the controlunit;

FIG. 10 depicts one embodiment of a request message used to identify acompatible control unit of an I/O processing system;

FIG. 11 depicts one embodiment of an accept message used to identify acompatible control unit of an I/O processing system;

FIG. 12 depicts one embodiment of a process for suspending I/Ooperations between a channel and a control unit;

FIG. 13 depicts one embodiment of a request message used to suspend I/Ooperations between a channel and a control unit;

FIG. 14 depicts one embodiment of an accept message used to respond tothe request message of FIG. 13; and

FIG. 15 depicts one embodiment of a computer program productincorporating one or more aspects of the present invention.

The detailed description explains the preferred embodiments of theinvention, together with advantages and features, by way of example withreference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with an aspect of the present invention, input/output(I/O) processing is facilitated. For instance, I/O processing isfacilitated by readily enabling processing of information between achannel and a control unit. I/O processing is facilitated, in oneexample, by providing a system and method for determining whether thechannel and the control unit are compatible with the same protocol.Further, I/O processing is facilitated, in another example, by providinga system and method for communicating between a control unit and achannel to suspend I/O operations.

In one exemplary embodiment, when the control unit is identified ascompatible with the protocol used by the channel, the channel mayinclude one or more commands in a block, referred to herein as atransport command control block (TCCB), an address of which is specifiedin a transport control word (TCW). The TCW is sent from an operatingsystem or other application to the I/O communications adapter, which inturn forwards the TCCB in a command message to the control unit forprocessing. The control unit processes each of the commands absent atracking of status relative to those individual commands by the I/Ocommunications adapter. The plurality of commands is also referred to asa channel program, which is parsed and executed on the control unitrather than the I/O communications adapter.

In an exemplary embodiment, the control unit generates a responsemessage in response to executing the channel program. The control unitmay also generate a response message without executing the channelprogram under a limited number of communication scenarios, e.g., toinform the I/O communications adapter that the channel program will notbe executed. The control unit may include a number of elements tosupport communication between the I/O communications adapter and I/Odevices, as well as in support of channel program execution. Forexample, the control unit can include control logic to parse and processmessages, in addition to one or more queues, timers, and registers tofacilitate communication and status monitoring. The I/O communicationsadapter parses the response message, extracting information, andperforms further operations using the extracted information.

One example of an I/O processing system incorporating and using one ormore aspects of the present invention is described with reference toFIG. 1. I/O processing system 100 includes a host system 101, whichfurther includes for instance, a main memory 102, one or more centralprocessing units (CPUs) 104, a storage control element 106, and achannel subsystem 108. The host system 101 may be a large scalecomputing system, such as a mainframe or server. The I/O processingsystem 100 also includes one or more control units 110 and one or moreI/O devices 112, each of which is described below.

Main memory 102 stores data and programs, which can be input from I/Odevices 112. For example, the main memory 102 may include one or moreoperating systems (OSs) 103 that are executed by one or more of the CPUs104. For example, one CPU 104 can execute a Linux® operating system 103and a z/OS® operating system 103 as different virtual machine instances.The main memory 102 is directly addressable and provides for high-speedprocessing of data by the CPUs 104 and the channel subsystem 108.

CPU 104 is the controlling center of the I/O processing system 100. Itcontains sequencing and processing facilities for instruction execution,interruption action, timing functions, initial program loading, andother machine-related functions. CPU 104 is coupled to the storagecontrol element 106 via a connection 114, such as a bidirectional orunidirectional bus.

Storage control element 106 is coupled to the main memory 102 via aconnection 116, such as a bus; to CPUs 104 via connection 114; and tochannel subsystem 108 via a connection 118. Storage control element 106controls, for example, queuing and execution of requests made by CPU 104and channel subsystem 108.

In an exemplary embodiment, channel subsystem 108 provides acommunication interface between host system 101 and control units 110.Channel subsystem 108 is coupled to storage control element 106, asdescribed above, and to each of the control units 110 via a connection120, such as a serial link. Connection 120 may be implemented as anoptical link, employing single-mode or multi-mode waveguides in a FibreChannel fabric. Channel subsystem 108 directs the flow of informationbetween I/O devices 112 and main memory 102. It relieves the CPUs 104 ofthe task of communicating directly with the I/O devices 112 and permitsdata processing to proceed concurrently with I/O processing. The channelsubsystem 108 uses one or more channel paths 122 as the communicationlinks in managing the flow of information to or from I/O devices 112. Asa part of the I/O processing, channel subsystem 108 also performs thepath-management functions of testing for channel path availability,selecting an available channel path 122 and initiating execution of theoperation with the I/O devices 112.

Each channel path 122 includes a channel 124 (channels 124 are locatedwithin the channel subsystem 108, in one example, as shown in FIG. 1),one or more control units 110 and one or more connections 120. Inanother example, it is also possible to have one or more dynamicswitches (not depicted) as part of the channel path 122. A dynamicswitch is coupled to a channel 124 and a control unit 110 and providesthe capability of physically interconnecting any two links that areattached to the switch. In another example, it is also possible to havemultiple systems, and therefore multiple channel subsystems (notdepicted) attached to control unit 110.

Also located within channel subsystem 108 are subchannels (not shown).One subchannel is provided for and dedicated to each I/O device 112accessible to a program through the channel subsystem 108. A subchannel(e.g., a data structure, such as a table) provides the logicalappearance of a device to the program. Each subchannel providesinformation concerning the associated I/O device 112 and its attachmentto channel subsystem 108. The subchannel also provides informationconcerning I/O operations and other functions involving the associatedI/O device 112. The subchannel is the means by which channel subsystem108 provides information about associated I/O devices 112 to CPUs 104,which obtain this information by executing I/O instructions.

Channel subsystem 108 is coupled to one or more control units 110. Eachcontrol unit 110 provides logic to operate and control one or more I/Odevices 112 and adapts, through the use of common facilities, thecharacteristics of each I/O device 112 to the link interface provided bythe channel 124. The common facilities provide for the execution of I/Ooperations, indications concerning the status of the I/O device 112 andcontrol unit 110, control of the timing of data transfers over thechannel path 122 and certain levels of I/O device 112 control.

Each control unit 110 is attached via a connection 126 (e.g., a bus) toone or more I/O devices 112. I/O devices 112 receive information orstore information in main memory 102 and/or other memory. Examples ofI/O devices 112 include card readers and punches, magnetic tape units,direct access storage devices, displays, keyboards, printers, pointingdevices, teleprocessing devices, communication controllers and sensorbased equipment, to name a few.

One or more of the above components of the I/O processing system 100 arefurther described in “IBM® z/Architecture Principles of Operation,”Publication No. SA22-7832-05, 6th Edition, April 2007; U.S. Pat. No.5,461,721 entitled “System For Transferring Data Between I/O Devices AndMain Or Expanded Storage Under Dynamic Control Of Independent IndirectAddress Words (IDAWS),” Cormier et al., issued Oct. 24, 1995; and U.S.Pat. No. 5,526,484 entitled “Method And System For Pipelining TheProcessing Of Channel Command Words,” Casper et al., issued Jun. 11,1996, each of which is hereby incorporated herein by reference in itsentirety. IBM is a registered trademark of International BusinessMachines Corporation, Armonk, New York, USA. Other names used herein maybe registered trademarks, trademarks or product names of InternationalBusiness Machines Corporation or other companies.

In one embodiment, to transfer data between F/O devices 112 and memory102, channel command words (CCWs) are used. A CCW specifies the commandto be executed, and includes other fields to control processing. Oneexample of a CCW is described with reference to FIG. 2 a. A CCW 200includes, for instance, a command code 202 specifying the command to beexecuted (e.g., read, read backward, control, sense and write); aplurality of flags 204 used to control the I/O operation; for commandsthat specify the transfer of data, a count field 206 that specifies thenumber of bytes in the storage area designated by the CCW to betransferred; and a data address 208 that points to a location in mainmemory that includes data, when direct addressing is employed, or to alist (e.g., contiguous list) of modified indirect data address words(MIDAWs) to be processed, when modified indirect data addressing isemployed. Modified indirect addressing is further described in U.S.application Ser. No. 11/464,613, entitled “Flexibly Controlling TheTransfer Of Data Between Input/Output Devices And Memory,” Brice et al.,filed Aug. 15, 2006, which is hereby incorporated herein by reference inits entirety.

One or more CCWs arranged for sequential execution form a channelprogram, also referred to herein as a CCW channel program. The CCWchannel program is set up by, for instance, an operating system, orother software. The software sets up the CCWs and obtains the addressesof memory assigned to the channel program. An example of a CCW channelprogram is described with reference to FIG. 2 b. A CCW channel program210 includes, for instance, a define extent CCW 212 that has a pointer214 to a location in memory of define extent data 216 to be used withthe define extent command. In this example, a transfer in channel (TIC)218 follows the define extent command that refers the channel program toanother area in memory (e.g., an application area) that includes one ormore other CCWs, such as a locate record 217 that has a pointer 219 tolocate record data 220, and one or more read CCWs 221. Each read CCW 220has a pointer 222 to a data area 224. The data area includes an addressto directly access the data or a list of data address words (e.g.,MIDAWs or IDAWs) to indirectly access the data. Further, CCW channelprogram 210 includes a predetermined area in the channel subsystemdefined by the device address called the subchannel for status 226resulting from execution of the CCW channel program.

The processing of a CCW channel program is described with reference toFIG. 3, as well as with reference to FIG. 2 b. In particular, FIG. 3shows an example of the various exchanges and sequences that occurbetween a channel and a control unit when a CCW channel program isexecuting. The link protocol used for the communications is FICON (FibreConnectivity), in this example. Information regarding FICON is describedin “Fibre Channel Single Byte Command Code Sets-3 Mapping Protocol(FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003), which ishereby incorporated herein by reference in its entirety.

Referring to FIG. 3, a channel 300 opens an exchange with a control unit302 and sends a define extent command and data associated therewith 304to control unit 302. The command is fetched from define extent CCW 212(FIG. 2 b) and the data is obtained from define extent data area 216.The channel 300 uses TIC 218 to locate the locate record CCW and theread CCW. It fetches the locate record command 305 (FIG. 3) from thelocate record CCW 217 (FIG. 2 b) and obtains the data from locate recorddata 220. The read command 306 (FIG. 3) is fetched from read CCW 221(FIG. 2 b). Each is sent to the control unit 302.

The control unit 302 opens an exchange 308 with the channel 300, inresponse to the open exchange of the channel 300. This can occur beforeor after locate command 305 and/or read command 306. Along with the openexchange, a response (CMR) is forwarded to the channel 300. The CMRprovides an indication to the channel 300 that the control unit 302 isactive and operating.

The control unit 302 sends the requested data 310 to the channel 300.Additionally, the control unit 302 provides the status to the channel300 and closes the exchange 312. In response thereto, the channel 300stores the data, examines the status and closes the exchange 314, whichindicates to the control unit 302 that the status has been received.

The processing of the above CCW channel program to read 4 k of datarequires two exchanges to be opened and closed and seven sequences. Thetotal number of exchanges and sequences between the channel and controlunit is reduced through collapsing multiple commands of the channelprogram into a TCCB. The channel, e.g., channel 124 of FIG. 1, uses aTCW to identify the location of the TCCB, as well as locations foraccessing and storing status and data associated with executing thechannel program. The TCW is interpreted by the channel and is not sentor seen by the control unit.

One example of a channel program to read 4 k of data, as in FIG. 2 b,but includes a TCCB, instead of separate individual CCWs, is describedwith reference to FIG. 4. As shown, a channel program 400, referred toherein as a TCW channel program, includes a TCW 402 specifying alocation in memory of a TCCB 404, as well as a location in memory of adata area 406 or a TIDAL 410 (i.e., a list of transfer mode indirectdata address words (TIDAWs), similar to MIDAWs) that points to data area406, and a status area 408. TCWs, TCCBs, and status are described infurther detail below.

The processing of a TCW channel program is described with reference toFIG. 5. The link protocol used for these communications is, forinstance, Fibre Channel Protocol (FCP). In particular, three phases ofthe FCP link protocol are used, allowing host bus adapters to be usedthat support FCP to perform data transfers controlled by CCWs. FCP andits phases are described further in “Information Technology—FibreChannel Protocol for SCSI, Third Version (FCP-3),” T10 Project 1560-D,Revision 4, Sep. 13, 2005, which is hereby incorporated herein byreference in its entirety.

Referring to FIG. 5, a channel 500 opens an exchange with a control unit502 and sends TCCB 504 to the control unit 502. In one example, the TCCB504 and sequence initiative are transferred to the control unit 502 in aFCP command, referred to as FCP_CMND information unit (IU) or atransport command IU. The control unit 502 executes the multiplecommands of the TCCB 504 (e.g., define extent command, locate recordcommand, read command as device control words (DCWs)) and forwards data506 to the channel 500 via, for instance, a FCP_Data IU. It alsoprovides status and closes the exchange 508. As one example, finalstatus is sent in a FCP status frame that has a bit active in, forinstance, byte 10 or 11 of the payload of a FCP_RSP IU, also referred toas a transport response IU. The FCP_RSP_IU payload may be used totransport FICON ending status along with additional status information,including parameters that support the calculation of extendedmeasurement words and notify the channel 500 of the maximum number ofopen exchanges supported by the control unit 502.

In a further example, to write 4 k of customer data, the channel 500uses the FCP link protocol phases, as follows:

1. Transfer a TCCB in the FCP_CMND IU.

2. Transfer the IU of data, and sequence initiative to the control unit502.

3. Final status is sent in a FCP status frame that has a bit active in,for instance, byte 10 or 11 of the FCP_RSP IU Payload. The FCP_RSP_INFOfield or sense field is used to transport FICON ending status along withadditional status information, including parameters that support thecalculation of extended measurement words and notify the channel 500 ofthe maximum number of open exchanges supported by the control unit 502.

By executing the TCW channel program of FIG. 4, there is only oneexchange opened and closed (see also FIG. 5), instead of two exchangesfor the CCW channel program of FIG. 2 b (see also FIG. 3). Further, forthe TCW channel program, there are three communication sequences (seeFIGS. 4-5), as compared to seven sequences for the CCW channel program(see FIGS. 2 b-3).

The number of exchanges and sequences remain the same for a TCW channelprogram, even if additional commands are added to the program. Compare,for example, the communications of the CCW channel program of FIG. 6with the communications of the TCW channel program of FIG. 7. In the CCWchannel program of FIG. 6, each of the commands (e.g., define extentcommand 600, locate record command 601, read command 602, read command604, read command 606, locate record command 607 and read command 608)are sent in separate sequences from channel 610 to control unit 612.Further, each 4 k block of data (e.g., data 614-620) is sent in separatesequences from the control unit 612 to the channel 610. This CCW channelprogram requires two exchanges to be opened and closed (e.g., openexchanges 622, 624 and close exchanges 626, 628), and fourteencommunications sequences. This is compared to the three sequences andone exchange for the TCW channel program of FIG. 7, which accomplishesthe same task as the CCW channel program of FIG. 6.

As depicted in FIG. 7, a channel 700 opens an exchange with a controlunit 702 and sends a TCCB 704 to the control unit 702. The TCCB 704includes the define extent command, the two locate record commands, andthe four read commands in DCWs, as described above. In response toreceiving the TCCB 704, the control unit 702 executes the commands andsends, in a single sequence, the 16 k of data 706 to the channel 700.Additionally, the control unit 702 provides status to the channel 700and closes the exchange 708. Thus, the TCW channel program requires muchless communications to transfer the same amount of data as the CCWchannel program of FIG. 6.

In an exemplary embodiment, the CCW channel program of FIG. 6 isimplemented using a protocol that supports Command Control Words, forexample, a Fibre Connectivity (FICON) protocol. Links operating underthis protocol may be referred to as being in a “Command Mode”.

In an exemplary embodiment, the TCW channel program of FIG. 7 isimplemented using a protocol to execute Transport Control Words, forexample, the Transport Mode protocol.

Turning now to FIG. 8, one embodiment of the control unit 110 and thechannel 124 of FIG. 1 that support TCW channel program execution aredepicted in greater detail. The control unit 110 includes CU controllogic 802 to parse and process command messages containing a TCCB, suchas the TCCB 704 of FIG. 7, received from the channel 124 via theconnection 120. The CU control logic 802 can extract DCWs and controldata from the TCCB received at the control unit 110 to control a device,for instance, I/O device 112 via connection 126. The CU control logic802 sends device commands and data to the I/O device 112, as well asreceives status information and other feedback from the I/O device 112.

The CU control logic 802 can access and control other elements withinthe control unit 110, such as CU timers 806 and CU registers 808. The CUtimers 806 may include multiple timer functions to establish wait ordelay time periods, such as those time periods used in suspending I/Ooperations. The CU timers 806 may further include one or more countdowntimers to monitor and abort I/O operations and commands that do notcomplete within a predetermined period. The CU registers 808 can includefixed values that provide configuration and status information, as wellas dynamic status information that is updated as commands are executedby the CU control logic 802. The control unit 110 may further includeother buffer or memory elements (not depicted) to store multiplemessages or status information associated with communications betweenthe channel 124 and the I/O device 112.

The channel 124 in the channel subsystem 108 includes multiple elementsto support communication with the control unit 110. For example, thechannel 124 may include CHN control logic 810 that interfaces with CHNsubsystem timers 812 and CHN subsystem registers 814. In an exemplaryembodiment, the CHN control logic 810 controls communication between thechannel subsystem 108 and the control unit 110. The CHN control logic810 may directly interface to the CU control logic 802 via theconnection 120 to send commands and receive responses, such as transportcommand and response IUs. Alternatively, messaging interfaces and/orbuffers (not depicted) can be placed between the CHN control logic 810and the CU control logic 802. The CHN subsystem timers 812 may includemultiple timer functions to, for example, establish wait or delay timeperiods. The CHN subsystem timers 812 may further include one or morecountdown timers to monitor and abort command sequences that do notcomplete within a predetermined period. The CHN subsystem registers 814can include fixed values that provide configuration and statusinformation, as well as dynamic status information, updated as commandsare transported and responses are received.

In some exemplary embodiments, the control unit 110 and the channel 124of FIG. 1 may operate in different modes, i.e., use different protocols.For example, the channel 124 may operate in the Transport Mode andutilize the transport mode protocol, and the control unit 110 mayoperate in the Command Mode and utilize the FICON protocol. The controlunit 110 and the channel 124 may each support the Command Mode and/orthe Transport Mode.

In order to successfully complete an I/O operation, a Transport Modecompatible channel 124, i.e., “Transport Mode channel”, should be ableto determine whether a control unit 110 of interest is also TransportMode compatible. This determination, and corresponding identification ofTransport Mode control units 110, should be able to be performed withoutdisrupting operations or causing problems in control units 110 thatsupport other protocols or modes.

In one exemplary embodiment, there is provided a system and method toallow the channel 124 to identify a compatible control unit 110, i.e., acontrol unit that supports a mode in which the channel 124 operates. Thechannel 124 may use a message in a first mode, such as the Command Mode,in combination with at least another message, to determine whether thecontrol unit supports a second mode, for example, the Transport Mode. Inan exemplary embodiment, the message in the first mode is a Request NodeIdentification (RNID) message. A RNID message may be used by the channel124 to request identification information from the control unit 110, andto initiate a link with the control unit 110.

The channel may receive a response to the message, such as a RNIDresponse, that includes data indicating whether the control unitsupports a selected message protocol. In an exemplary embodiment, theselected message protocol is a Process Log-in (PRLI) and Process Log-out(PRLO) message protocol, which may be referred to as “PRLI/PRLO”. In anexemplary embodiment, an unused bit may be defined in a field in theRNID response, such as the Node Parameters field, that informs thechannel if the control unit does or does not support PRLI/PRLO. PRLImessages may be used to establish service parameters between the channel124 and the control unit 110, and PRLO messages may be used toinvalidate existing service parameters so that new service parametersmay be re-established.

RNID, PRLI and PRLO commands and responses are extended link service(ELS) messages. The Process Log-in and Process Log-out Extended Linkservice may be defined by Fibre Channel Framing and Signaling protocol(FC-FS), which is described further in “FIBRE CHANNEL FRAMING ANDSIGNALING (FC-FS) REV 1.70; NCITS working draft proposed AmericanNational Standard Information Technology”, Feb. 8, 2002, which is herebyincorporated herein by reference in its entirety. The Request NodeIdentification Extended Link service may be defined by Fiber Channelsingle byte protocol, which is described in “Fibre Channel Single ByteCommand Code Sets-3 Mapping Protocol (FC-SB-3), T11/Project 1357-D/Rev.1.6, INCITS (March 2003), referenced above and incorporated herein byreference in its entirety.

Once the channel 124 determines that the control unit 110 supportsPRLI/PRLO, then a PRLI message is used by the channel 124 to determineif the control unit 110 supports the Transport Mode. If the control unit110 does support the Transport Mode, the PRLI message is used toestablish the required initial Transport Mode operating parameters.

In another exemplary embodiment, there is provided a system and methodthat allows one of the channel 124 or the control unit 110 (referred toas the “sender”) to inform the other (referred to as the “receiver”)that it will not accept new I/O operations for a selected period oftime, and thereby instruct the receiver to suspend initiation of I/Ooperations for the period of time. The period of time may be specifiedby the sender. In one embodiment, this information is provided via aPRLO message, which specifies the period of time for suspension.

Turning now to FIG. 9, a process 900 for identifying a compatiblecontrol unit 110 of an I/O processing system using data from the controlunit 110 will now be described in accordance with exemplary embodiments,and in reference to the I/O processing system 100 of FIG. 1.

At block 902, the channel 124 sends a message to the control unit 110.In one exemplary embodiment, the message is a message that requestsidentification information, such as a RNID command.

At block 904, the control unit 110 may respond to the message, forexample, in the form of a RNID Response. In one exemplary embodiment, abit may be added in the RNID response. This bit informs the channel thatthe control unit 110 supports the selected message protocol.

In one example, the selected message protocol is a PRLI/PRLO protocol.The channel may identify a control unit that supports the PRLI/PRLO witha RNID command. A value for a bit in the RNID response may be set toindicate to the channel 124 that that control unit 110 supportsPRLI/PRLO. For example, for a RNID response in the Fibre Channel singlebyte protocol, a bit may be used to identify compatibility, especially abit that has been reserved in previous protocols.

For example, byte 1 (protocol byte), bit 3, (bits 3 to 7 have beenreserved in previous protocols such as Command Mode protocols), of theNode Parameters field of the RNID response may be used to identify thecontrol unit 110 as capable of supporting a Process Login with a CommandMode code. The value of bits 0, 1 and 2 of this byte are not changedrelative to previous protocols. By default, previous Command Modecontrol units will not turn this bit on in the Node Parameter field ofthe response to the RNID, thus informing the channel that the controlunit does not support PRLI. This bit in the RNID response may be ignoredby a non-Transport Mode capable channel 124.

At block 906, the channel 124 determines from the response (e.g., theRNID response) whether the control unit supports the selected messageprotocol (e.g., PRLI/PRLO).

At block 908, the channel 124 sends a message using the selected messageprotocol, such as a PRLI message, to determine whether the control unit110 supports a selected mode, such as Transport Mode. In one exemplaryembodiment, a data field is provided in which data may be included in amessage in response to a command that indicates whether the modesupported by the channel is also supported by the control unit. The datamay indicate to the channel 124 whether the control unit 110 can supportthe Transport Mode.

In an exemplary embodiment, the PRLI request is transmitted from thechannel 124 to the control unit 110 to identify to the control unit 110the capabilities that the channel 124 expects to use with the controlunit 110 and to determine the capabilities of the control unit 110. Inone exemplary embodiment, PRLI is used only to establish serviceparameters; it is not used to establish image pairs (e.g., logicalrepresentations of pairs of control units 110 and channels 124) andtherefore all fields defined for establishing image pairs and processassociaters are not used and are set to 0. Image pair establishment maybe accomplished using an Establish Logical Path (ELP) function. Theoperating parameters negotiated during Process Login apply to alllogical paths currently established or to be established between thechannel 124 and the control unit 110.

In an exemplary embodiment, if the process login state is ever reset,the channel 124 will start with an RNID message to check for PRLI/PRLOsupport before resending PRLI to re-establish the service parameters.During link initialization, the Process Login function may be performedafter N-Port Login and RNID but before establishment of logical paths.In some recovery scenarios, the PRLI can occur with logical pathsalready established. The state of the logical paths will not be affectedwhen this occurs.

At block 910, the control unit 110 sends a response using the selectedmessage protocol. For example, the control unit 110 may send a PRLIresponse to the channel 124. If the bit is not set in the PRLI responsethen the channel 124 may not attempt a Process Login to the control unit110 and the control unit 110 may not be marked as Transport Modecapable.

In an exemplary embodiment, in response to the PRLI request, the controlunit 110 sends a “PRLI Accept” message to the channel 124 that reportsthe capabilities of the control unit 110 to the channel 124. An acceptresponse code indicating other than REQUEST EXECUTED may be provided ifa Transport Mode Service Parameter page of the PRLI message isincorrect. A Link Service Reject (LS_RJT) may be used to indicate thatthe PRLI request is not supported or is incorrectly formatted. PRLIaccept response codes may be defined in the FC-FS protocol.

At block 912, if the data in the response from the control unit 110(e.g., the bit set in the PRLI response message) indicates that thecontrol unit supports the Transport Mode, the channel 124 may proceed toexchange Command Mode and/or Transport Mode parameters, and initiate I/Ooperations in the Transport Mode.

Turning now to FIG. 10, an example of a PRLI Request message 1000 isdepicted. The payload of the PRLI request 1000 may include one or moreservice parameter pages, each of which include service parameters for asingle image pair.

The service parameter page of the PRLI Request message 1000 may includemultiple fields, such as type code 1002, type extension 1004, maximuminitiation delay time 1006 and flags 1008. Each field in the page of thePRLI Request message 1000 is assigned to a particular byte address.Although one arrangement of fields within the page of the PRLI Requestmessage 1000 is depicted in FIG. 10, it will be understood that theorder of fields can be rearranged to alternate ordering within the scopeof the disclosure. Moreover, fields in the page of the PRLI Requestmessage 1000 can be omitted or combined within the scope of theinvention.

The type code field 1002, located at word 0, byte 0, represents theprotocol type code, such as the Fibre Channel Single Byte Protocol typecode. For example, a value of hex “1B” in this byte indicates that thisservice parameter page 1000 is defined in the selected protocol (e.g.Fiber Channel single byte).

The maximum initiation delay time field 1004, located at word 3, byte 0,provides the maximum time (e.g. in seconds) that the channel 124 canallow in the Initiation Delay Time field in a process Logout (PRLO) fromthe control unit. Initiation delay time is further described below. Word3, bytes 1 and 3 may be reserved and set to zero.

Flags 1008, in an exemplary embodiment, has the following definition:

Bit 0—Transport Mode/Command Mode. A value of this bit set to one (1)means that the sender supports both Command Mode (e.g. FICON) andTransport Mode. If the bit is set to zero (0), the sender only supportsCommand Mode. If the channel 124 sets this bit to a one, then thecontrol unit 110 may respond with this bit set to one if it supports theTransport Mode.

Bits 1-6—Reserved.

Bit 7—First Transfer Ready for Data Disabled. If both the channel 124and control unit 110 choose to disable the first write FCP_XFER_RDY IU,then all I/O operations performing writes between the channel andcontrol unit shall operate without using the FCP_XFER_RDY IU before thefirst FCP_DATA IU. The FCP_XFER_RDY IU is transmitted to request eachadditional FCP_DATA IU, if any.

In one exemplary embodiment, the remaining fields in the page of thePRLI Request message 1000 may be reserved and/or set to zero (0). Forexample, bytes 2 and 3 of word 0, and words 1 and 2 are set to zero.Bytes 1 and 2 of word 3 may also be reserved.

Turning now to FIG. 11, an example of a PRLI Accept message 1100 isdepicted. The payload of the PRLI Accept message 1100 may include one ormore service parameter pages, each of which include service parametersfor a single image pair.

The service parameter page of the PRLI Accept message 1100 may includemultiple fields, such as type code 1102, type extension 1104, responsecode 1106, first burst size 1108 and flags 1110. Each field in the pageof the PRLI Accept message 1100 is assigned to a particular byteaddress. Although one arrangement of fields within the page of the PRLIAccept message 1100 is depicted in FIG. 11, it will be understood thatthe order of fields can be rearranged to alternate ordering, or can beomitted or combined, within the scope of the disclosure.

The type code field 1102, located at word 0, byte 0, is the protocoltype code, and is similar to the type code field 1002 of FIG. 10.

The response code field, located at word 0, byte 2, bits 4-7, and isdefined by its corresponding protocol, such as the FC-FS protocol.

The First Burst Size field 1108, located at word 3, bytes 0-1, bits0-15, provides the maximum amount of data (e.g., the maximum number of 4k byte blocks of data) allowed in the first DATA IU that is sentimmediately after the first transmission control IU (TC_IU), when theFirst Transfer Ready for Data Disabled flag bit (word 3, byte 3, bit 7)is set to one. A value of zero in this field indicates that there is nofirst burst size limit. Word 3 byte 2 is reserved.

Flags 1110 are similar to the flags 1008 of FIG. 10 described inconjunction with the PRLI Request. The control unit 110 sets values tothese flags that correspond to the mode of operation it will run withthe channel.

In one exemplary embodiment, the remaining fields in the page of thePRLI Accept message 1100 may be reserved and/or set to zero (0). Forexample, bits 1-3 of word 0, byte 2, and words 1 and 2 are set to zero.Byte 3 of word 0 is reserved and set to zero. Byte 2 of word 3 may alsobe reserved.

The following is an example of a procedure used by the channel 124 toidentify the mode capability of a targeted control unit 110. In thisexample, the channel 124, operating in the Transport Mode, uses RNID andPRLI messages in a Log in procedure to identify mode capability. Thisprocedure may occur before any I/O operations are attempted by thechannel 124 to the control unit 110. The exemplary procedure is asfollows:

1. Perform a Fabric Login.

2. Perform a N_Port Login.

3. Attempt a RNID. The channel 124 sends an RNID message to determinewhether the control unit 110 supports PRLI/PRLO. If the RNID fails(e.g., the channel's RNID response timer times out or the channel 124receives a fabric reject), I/O operations will not be driven to thecontrol unit 110 until some new I/O operation or channel drives a RNIDthat is successful.

If the RNID is successful, i.e., the channel 124 receives a validresponse, the channel 124 determines whether the control unit 110supports PRLI/PRLO. A successful RNID is any valid response from thecontrol unit 110, which may include, for example, a RNID response and aLink Service Reject.

4. If PRLI is supported, then the channel 124 initiates a PRLI message.If PRLI is not supported, the channel 124 may drive I/O operations inthe Command Mode (e.g., FICON). For example, the channel 124 may driveI/O operations after sending a successful Establish Logical Path (ELP)link control IU.

5. If the channel 124 receives a response from the control unit 110indicating that transport mode is supported, the channel 124 mayinitiate I/O operations to the control unit 110 in either the CommandMode or the Transport Mode. In one embodiment, I/O operations areinitiated after a successful ELP IU.

Turning now to FIG. 12, a process 1200 for suspending I/O operationsbetween the channel 124 and the control unit 110 will now be describedin accordance with exemplary embodiments, and in reference to the I/Oprocessing system 100 of FIG. 1.

At block 1202, the channel 124 or the control unit 110, which has a needto hold off I/O operations for a period of time, may use a message suchas a PRLO message to suspend operations. The channel 124 or control unit110 that sends a PRLO message is referred to herein as the “sender”. Thechannel or control unit that receives (or is intended to receive) thePRLO message is referred to herein as the “receiver”.

At block 1204, the receiver receives the PRLO message and suspends allI/O operations for a period of time specified in the PRLO message. Forexample, if the control unit 110 receives the PRLO, it suspends I/Ooperations such as status messages. In another example, if a channel 124receives the PRLO, it suspends I/O operations such as read or writecommands.

At block 1206, in one exemplary embodiment, during the suspensionperiod, the channel 124 or the control unit 110 may re-establish serviceparameters between the channel 124 and control unit 110 if desired. Thisallows the channel 124 or the control unit 110 to perform whateverinternal functions are required without causing the loss of the logicalpaths or alerts such as interface control checks (IFCCs).

At block 1208, after the period of time specified in the PRLO, thechannel 124 may re-initiate the link between the channel 124 and thecontrol unit 110. In an exemplary embodiment, the channel 124 executes aRNID and then a Process Log In, and if both are successful, proceedswith normal I/O operations.

Turning now to FIG. 13, an example of a PRLO Request message 1300 isdepicted. The payload of the PRLO Request 1300 may include one or moreservice parameter pages, each of which include service parameters for asingle image pair.

The service parameter page of the PRLI Request 1300 may include multiplefields, such as type code 1302, type extension 1304, and initiationdelay time 1306. Each field in the page 1300 is assigned to a particularbyte address. Although one arrangement of fields within the page of thePRLI Request 1300 is depicted in FIG. 13, it will be understood that theorder of fields can be rearranged to alternate ordering within the scopeof the disclosure. Moreover, fields in the page of the PRLI Request 1300can be omitted or combined within the scope of the invention.

The type code field 1302, located at word 0, byte 0, is the protocoltype code, and is similar to the type code field 1002 of FIG. 10described in the PRLI Request.

The initiation delay time field 1306, located at word 3, byte 0,indicates the amount of time that the receiver should wait beforeinitiating any new I/O operations. If the PRLO is sent by the controlunit 110, the delay time field 1306 indicates the wait time in secondsbefore the channel may attempt PRLI to re-establish new operatingparameters between the channel 124 and the control unit 110. If the PRLOis sent by the channel 124, the delay time field 1306 is set to a valuethat the channel 124 wants the control unit 110 to wait before sendingI/O messages such as unsolicited status messages or Test Initializationlink control (TIN) messages. This time limit may be based on thechannel's ability to delay sending I/O operation messages to the controlunit 110 without causing higher levels of recovery to occur. During thetime specified in the delay time field 1306, the channel 124 will notstart any new Transport Mode or Command Mode I/O operations to thecontrol unit. In one exemplary embodiment, the maximum value that can beset is specified by the Maximum Initiation Delay Time 1004 set by thechannel 124 in the PRLI Request message 1000.

In one exemplary embodiment, the remaining fields in the page 1300 maybe reserved and/or set to zero (0). For example, bytes 2 and 3 of word0, and words 1 and 2 are set to zero. Bytes 1-3 of word 3 may also bereserved.

Turning now to FIG. 14, an example of a PRLO Accept message 1400 isdepicted. The payload of the PRLO Accept message 1400 may include one ormore service parameter pages, each of which include service parametersfor a single image pair.

The service parameter page of the PRLO Accept message 1400 may includemultiple fields, such as type code 1402, type extension 1404, andresponse code 1406. Each field in the page of the PRLO Accept 1400 isassigned to a particular byte address. Although one arrangement offields within the page of the PRLO Accept 1400 is depicted in FIG. 14,it will be understood that the order of fields can be rearranged toalternate ordering, or can be omitted or combined, within the scope ofthe disclosure.

The type code field 1402, located at word 0, byte 0, is the protocoltype code, and is similar to the type code field 1102 of the PRLIAccept.

The response code field 1406, located at word 0, byte 2, bits 4-7, isdefined by its corresponding protocol, such as the FC-FS protocol.

In one exemplary embodiment, the remaining fields in the page of thePRLO Accept 1400 may be reserved and/or set to zero (0). For example,bits 1-3 of word 0, byte 2, and words 1 and 2 are set to zero. Byte 3 ofword 0 is reserved and set to zero. Also, word 3 may be reserved.

The following is an example of a procedure used by the channel 124 toinstruct or request suspension of I/O operations from the control unit110. In this example, the channel 124 sends a PRLO message to thecontrol unit to suspend I/O operations. The procedure is as follows:

1. The channel 124 first stops driving all new Command Mode andTransport Mode operations.

2. The channel 124 may wait a selected amount of time, such as theamount of time specified in the Command Mode protocol, to allow pendingoperations to complete.

3. The channel 124 sends a PRLO to the control unit with a period oftime defined in the Initiation Delay Time field 1306.

4. The control unit 110 receives the PRLO, and in response performs oneor more of the following:

-   -   4(a). Responding to all new Command Mode or Transport Mode        commands from the channel 124 with busy messages.    -   4(b). Completing all active Command Mode operations and        completing or terminating all active Transport Mode operations        from the channel 124. The control unit 110 may then wait for a        selected time period, such as 100 ms.    -   4(b). The control unit 110 then responds with the PRLO Accept        message 1400 (“PRLO_ACC”).

During the time period specified in the initiation delay time field1306, the control unit 110 will not attempt to present any unsolicitedI/O operation messages, such as asynchronous status messages, to thechannel 124 until after at least the channel 124 initiates new I/Ooperations (e.g., a new PRLI is sent from the channel 124) or until theInitiative Delay Time has passed. If or when the control unit 110detects a state change, the control unit will not attempt to send a TINuntil after the Initiative Delay Time period has passed.

5. After the channel 124 receives the PRLO_ACC, the channel may wait foranother selected time period (e.g., 100 milliseconds) and then abort allactive exchanges to the control unit 110. The channel 124 may thenperform any functions needed that prompted the PRLO.

6. In an exemplary embodiment, the channel 124 may then re-initiate alink with the control unit 110 by sending an RNID to the control unit110. The channel 124 may not proceed until a successful response hasbeen received for the RNID. After a certain number of unsuccessfulattempts (e.g., four attempts), the channel 124 may remove all logicalpaths locally and drive a state change directly to the control unit 110.In an exemplary embodiment, the channel 124 will attempt to perform anEnd port to End port Registered State Change Notification (RSCN), orother function to indicate to the control unit that a state change hasoccurred.

7. The control unit 110 may respond to the RNID by indicating whether itsupports PRLI/PRLO.

8. If the control unit 110 supports PRLI/PRLO, the channel 124 may senda PRLI to the control unit 110. The PRLI may include all parameters perthe Transport Mode and may not proceed until a successful response hasbeen received for the PRLI. The control unit 110 responds with the PRIACC response. If a state change event did occur, the control unit 110may send the required TIN independent of the Initiation Delay Timeperiod.

9. In an exemplary embodiment, if the control unit 110 does not supportPRLI/PRLO, then all of the Transport Mode operations that the channel124 may have queued up are returned to the OS 103 with a program checkand a related alert, such as a Subchannel-Status Extension field reasoncode: “Transport Mode not supported by the CU”.

10. The channel 124 is now ready to drive new I/O operations to thecontrol unit 110.

The following is an example of a procedure used by the control unit 110to instruct or request suspension of I/O operations from the channel124. In this example, the control unit 110 sends a PRLO message to thecontrol unit to suspend I/O operations. The procedure is as follows:

1. First, the control unit 110 may return busy signals for any messagesregarding new I/O operations, and may complete or terminate all pendingTransport Mode and Command Mode operations.

2. The control unit 110 sends a PRLO to the channel 124 with a period oftime defined in the Initiation Delay Time field 1306.

3. The channel 124 stops driving new Command Mode and Transport Modeoperations and waits a selected time period (e.g., at least 100 ms)before responding with a PRLO ACC. The channel 124 may also complete orterminate all pending operations, and then abort any exchanges that arestill active and generate an alert such as an interface control check(IFCC) interrupt for each exchange aborted.

4. The channel 124 waits the Initiative Delay Time period.

5. The channel 124 then sends the RNID message and does not proceed withChannel Mode or Transport Mode operations until a successful responsefrom the control unit 110 has been received for the RNID. This processis similar to the process used when initiating the link for the firsttime.

6. The control 110 unit may respond to the RNID by indicating whether itsupports PRLI/PRLO.

7. If the control unit 110 supports PRLI/PRLO, the channel 124 sends aPRLI to the control unit 110. The PRLI may include all parameters perthe Transport Mode and may not proceed until a successful response hasbeen received for the PRLI. The control unit 110 may respond with thePRLI Accept response 1400.

8. In an exemplary embodiment, if a state change is received anytimebetween the PRLO and a successful PRLI, the channel 124 will drive aTIN. If the TIN is unsuccessful, then the logical paths may be removedand re-established before new I/O operations are initiated.

9. In an exemplary embodiment, if the PRLI is not successful, or if thecontrol unit does not support PRLI/PRLO, then all of the Transport Modeoperations that the channel 124 may have queued up are returned to theOS 103 with a program check and a related alert, such as aSubchannel-Status Extension field reason code: “Transport Mode notsupported by the CU”.

10. The channel 124 is now ready to drive new I/O operations to thecontrol unit 110.

The following is an example of a procedure used by the control unit 110to change operating parameters. Although this exemplary procedure isdescribed as being performed by the control unit 110, it may also beperformed by the channel 124. This procedure incorporates the use of thePRLO message. The PRLO, RNID and PRLI may be used by the control unit110 to dynamically change the operating parameters without interferingwith ongoing system operations and without losing the logical paths thatwere previously established. The procedure is as follows:

1. To change the operating parameters the control unit 110 sends aProcess Log out with a time period set in the Initiation Delay Timefield 1306.

2. The control unit 110 may perform any required or desired changes inoperating parameters or perform any updates needed or desired.

3. In response to the PRLO, the channel 124 suspends I/O operations forthe period specified in the Delay Time field 1306, and thereafterinitiates a new Process Log in to establish the new parameters.

For example, if a logical connection has been made between a TransportMode capable channel 124 and the control unit 110, and the control unit110 needs to perform an update, such as a Licensed Internal Code (LIC)back-off to a code load that does not support Transport Mode, or needsto perform a LIC code update that now supports Transport Mode, thecontrol unit 110 first sends a Process Log out as in the exampledescribed above.

The control unit 110 may perform the code update after sending the PRLO.

The channel 124 suspends all new work to the control unit 110 and waitsthe amount of time specified in the PRLO message, before sending a RNIDto the control unit 110. In an exemplary embodiment, only if the bit isset in the RNID response that indicates support for PRLI will thechannel send a PRLI to the control unit 110 as part of re-establishing alink with the control unit 110. This allows a code reload to workindependent of a level change, either forward or backward relative tosupporting or not supporting Transport Mode.

If the control unit 110 no longer supports Transport Mode, the channel124 will return all the Transport Mode I/O operations for the controlunit 110 to the OS 103 with a program check and a related alert, such asa Subchannel-Status Extension field reason code: “Transport Mode notsupported by the CU”. The Transport Mode I/O operations being returnedto the OS 103 may inform the OS 103 that the control unit 110 no longersupports Transport Mode.

In an exemplary embodiment, if a control unit's code is updated fromsupporting only Command Mode to supporting Transport Mode, the controlunit 110 will transmit a State Change command to the channel 124. Thiswill cause a channel 124 that supports Transport Mode to send an RNIDbefore the channel 124 sends the TIN message. The RNID accept from thecontrol unit 110 informs the channel 124 that the control unit nowsupports PRLI/PRLO. This will cause the channel 124 to send the PRLI tothe control unit 110 and discover that the control unit 110 supportsTransport mode. This will now allow the channel 124 to accept Transportmode I/O operations for the control unit 110.

In an exemplary embodiment, the control unit 110 may also generate asummary status to the OS 103. This will result in the operating systemreading node descriptor data from the control unit 110 that will informthe operating system that the control unit 110 now supports TransportMode.

Technical effects of exemplary embodiments include the ability of thechannel subsystem to identify control units as compatible (e.g.,transport mode capable) without causing problems in an incompatible(e.g., command mode capable such as FICON) control unit that does notsupport the mode of the channel subsystem. Other technical effectsinclude the ability of the channel subsystem or the control unit todirect the suspension of I/O operations for a period of time.

The systems and methods described herein provide numerous advantages, inthat they provide an effective way for a channel to determine whether acontrol unit operates in a compatible mode. Additional advantagesinclude provision of an effective way for the control unit to suspendcommands without the use of busy messages or other responses that maycause errors in the I/O sequence. Further advantages include the abilityto exchange selected operating parameters between the control unit andthe channel.

For example, there is no link protocol using CCWs (e.g., FICON) thatincludes protocols for exchanging operating parameters required byprotocols using TCWs (e.g., transport mode protocol)). Furthermore,there is no protocol that allows either the channel or the control unitto inform the other that it wants to stop receiving requests for newwork for a selected period of time.

In prior art FICON protocols, for example, when the channel needs tosuspend operations, it will stop driving new work, i.e., sending newcommands for new I/O operations. When the control unit needs to suspendoperations, it will respond to commands for new work with a “busy”message. However, this response may result in an error such as aninterface timeout and an associated interface control check (IFCC),and/or result in the loss of the logical path established by, e.g., the“Establish Logical Path” (ELP) link control IU.

The systems and methods described herein overcome these disadvantagesand provide the advantages described above.

As described above, embodiments can be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. In exemplary embodiments, the invention is embodied incomputer program code executed by one or more network elements.Embodiments include a computer program product 1500 as depicted in FIG.15 on a computer usable medium 1502 with computer program code logic1504 containing instructions embodied in tangible media as an article ofmanufacture. Exemplary articles of manufacture for computer usablemedium 1502 may include floppy diskettes, CD-ROMs, hard drives,universal serial bus (USB) flash drives, or any other computer-readablestorage medium, wherein, when the computer program code logic 1504 isloaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. Embodiments include computerprogram code logic 1504, for example, whether stored in a storagemedium, loaded into and/or executed by a computer, or transmitted oversome transmission medium, such as over electrical wiring or cabling,through fiber optics, or via electromagnetic radiation, wherein, whenthe computer program code logic 1504 is loaded into and executed by acomputer, the computer becomes an apparatus for practicing theinvention. When implemented on a general-purpose microprocessor, thecomputer program code logic 1504 segments configure the microprocessorto create specific logic circuits.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another. Furthermore, the use ofthe terms a, an, etc. do not denote a limitation of quantity, but ratherdenote the presence of at least one of the referenced item.

1. A computer program product for processing communications between acontrol unit and a channel subsystem in an input/output processingsystem, comprising a tangible storage medium readable by a processingcircuit and storing instructions for execution by the processing circuitfor performing a method comprising: sending a Request NodeIdentification (RNID) message from the channel subsystem to the controlunit in a Command mode, wherein the Command mode uses a FibreConnectivity (FICON) protocol supporting Channel Command Words (CCWs);receiving a RNID response from the control unit, the RNID responsecomprising a Process Log-in (PRLI) indicator, the PRLI indicatorindicating whether the control unit supports a PRLI message protocol;responsive to the received PRLI indicator indicating a PRLI messageprotocol is not supported by the control unit, continuing operation inthe Command mode; responsive to the received PRLI indicator indicatingthe PRLI message protocol is supported by the control unit, sending aPRLI message to the control unit to determine whether the control unitsupports a Transport mode, wherein the Transport mode supports TransportCommand Control Blocks (TCCBs); and responsive to the PRLI messagedetermining that the control unit supports the Transport mode, settingthe operational parameters for the Transport mode for that control unit.2. The computer program product of claim 1, wherein the Transport modeuses a protocol supporting Transport Control Words (TCW).
 3. Thecomputer program product of claim 1, wherein the PRLI message protocolis a protocol that uses PRLI and process log-out (PRLO) messages.
 4. Thecomputer program product of claim 1, wherein the PRLI indicatorcomprises a bit in a field that indicates whether the PRLI messageprotocol is supported.
 5. The computer program product of claim 1,wherein the PRLI indicator comprises a data bit setting in a field ofthe RNID response that indicates whether the control unit supports thePRLI message protocol.
 6. The computer program product of claim 1,further comprising receiving a PRLI response from the control unit, anddetermining from the PRLI response whether the control unit supports theTransport mode.
 7. The computer program product of claim 6, whereindetermining whether the control unit supports the Transport modecomprises identifying a data bit setting in a field of the PRLIresponse.
 8. The computer program product of claim 7, wherein the fieldis a flags field of the PRLI response.
 9. The computer program productof claim 1, wherein: the PRLI indicator includes a bit in a field thatindicates whether the PRLI message protocol is supported; the Transportmode supports Transport Control Words (TCW); and the method furthercomprises initiating input/output operations to the control unit usingthe Transport mode.
 10. An apparatus for processing communications in aninput/output processing system, comprising: a channel subsystem of ahost computer system in communication with a control unit capable ofcommanding and determining status of an I/O device, the channelsubsystem performing: sending a Request Node Identification (RNID)message to the control unit in a Command mode, wherein the Command modeuses a Fibre Connectivity (FICON) protocol supporting Channel CommandWords (CCWs); receiving a RNID response from the control unit, the RNIDresponse comprising a Process Log-in (PRLI) indicator, the PRLIindicator indicating whether the control unit supports a PRLI messageprotocol; responsive to the received PRLI indicator indicating a PRLImessage protocol is not supported by the control unit, continuingoperation in the Command mode; responsive to the received PRLI indicatorindicating the PRLI message protocol is supported by the control unit,sending a PRLI message to the control unit to determine whether thecontrol unit supports a Transport mode, wherein the Transport modesupports Transport Command Control Blocks (TCCBs); and responsive to thePRLI message determining that the control unit supports the Transportmode, setting the operational parameters for the Transport mode for thatcontrol unit.
 11. The apparatus of claim 10, wherein the Transport modeuses a protocol supporting Transport Control Words (TCW).
 12. Theapparatus of claim 10, wherein the PRLI message protocol is a protocolthat uses PRLI and process log-out (PRLO) messages.
 13. The apparatus ofclaim 10, wherein the PRLI indicator comprises a bit in a field thatindicates whether the PRLI message protocol is supported.
 14. Theapparatus of claim 10, wherein determining whether the PRLI indicatorcomprises a data bit setting in a field of the RNID response thatindicates whether the control unit supports the PRLI message protocol.15. The apparatus of claim 10, further comprising receiving a PRLIresponse from the control unit, and determining from the PRLI responsewhether the control unit supports the Transport mode.
 16. The apparatusof claim 15, wherein determining whether the control unit supports theTransport mode comprises identifying a data bit setting in a field ofthe PRLI response.
 17. The apparatus of claim 16, wherein the field is aflags field of the PRLI response.
 18. The apparatus of claim 10,wherein: the PRLI indicator comprises a bit in a field that indicateswhether the PRLI message protocol is supported; the Transport modesupports Transport Control Words (TCW); and the channel subsystemfurther performs initiating input/output operations to the control unitusing the Transport mode.
 19. A method of processing communicationsbetween a control unit and a channel subsystem in an input/outputprocessing system, the method comprising: sending a Request NodeIdentification (RNID) message from the channel subsystem to the controlunit in a Command mode, wherein the Command mode uses a FibreConnectivity (FICON) protocol supporting Channel Command Words (CCWs);receiving a RNID response from the control unit, the RNID responsecomprising a Process Log-in (PRLI) indicator, the PRLI indicatorindicating whether the control unit supports a PRLI message protocol;responsive to the received PRLI indicator indicating a PRLI messageprotocol is not supported by the control unit, continuing operation inthe Command mode; responsive to the received PRLI indicator indicatingthe PRLI message protocol is supported by the control unit, sending aPRLI message to the control unit to determine whether the control unitsupports a Transport mode, wherein the Transport mode supports TransportCommand Control Blocks (TCCBs); and responsive to the PRLI messagedetermining that the control unit supports the Transport mode, settingthe operational parameters for the Transport mode for that control unit.20. The method of claim 19, wherein: the PRLI indicator includes a bitin a field that indicates whether the PRLI message protocol issupported; the Transport mode supports Transport Control Words (TCW);and the method further comprises initiating input/output operations tothe control unit using the Transport mode.